(1) Field of the Invention
The present invention relates to pneumatic tires for use under high internal pressures and heavy loads, and more particularly, the invention relates to results of development and research on heavy duty-high pressure pneumatic radial tires which are adapted for special uses, for instance, to be used under severe conditions, in such as running wheels used in aircraft and super high speed trains (linear motor cars, etc.).
(2) Related Art Statement
In order to meet the demand for a remarkably expanded amount of goods and substances to be transported under a recently conspicuous trend of energy saving, it is a priority problem how to satisfy need for weight reduction which have been up to now most required in tires for aircraft, etc.
In high internal pressure heavy duty pneumatic tires of this kind, bias construction carcasses have been principally employed to date. However, since these tires need a greater number of plies, they do not fit the tire weight reduction criteria. This is an origin from which radial tires have begun to be examined.
Japanese patent application Laid-open No. 61-71,206 mainly discloses how to select a material for reinforcing cords in a radial construction carcass, principally aiming at supplement of an insufficient shock-mitigating power of aircraft tires which originates from the replacement of a bias construction carcass by the radial construction carcass.
As compared with bias tires, the aircraft tires or heavy duty-high pressure pneumatic radial tires which are served in similar uses thereto are more advantageous with respect to weight reduction. However, since use conditions are severer in such tires, decisive reinforcing materials and structures have not been obtained yet, and are still under study and examination. From a standpoint of high speed durability, it is common to adopt an arrangement of a belt surrounding a carcass in which a plurality of belt cord layers including a layer of organic fiber cords are arranged at an angle near substantially 0.degree. with respect to the circumference of the crown of the carcass. For this purpose, an examination has been made of aromatic polyamide fibers, nylon, polyester, rayons etc. On the other hand, any special proposal has not been made with respect to carcasses including materials thereof excluding that the carcasses have come to be designed in a radial construction.
In radial tires of this kind, since a tension acts upon cords of the carcass ply due to deformation originating from application of high pressure air (10 to 16 kg/cm.sup.2) and a load, a pullout force is exerted upon a turn-up end portion of the carcass ply wound around a bead core at a bead portion and a shearing force acts between the ply layers of the carcass. These forces are repeatedly exerted upon the tire when the tire rolls, which leads to ply separation.
However, use of an additional reinforcement to cope with the ply separation, needless to say, is contradictory to the weight reduction of the tire.